Generally, vehicles include fuel tanks provided in order to accommodate various fuels required for driving of an engine. Among these fuel tanks, a fuel tank accommodating a liquid-phase fuel therein includes a liquid level sensor provided in order to allow a driver to recognize a residual amount of fuel.
The liquid level sensor of the fuel tank is classified into a mechanical liquid level sensor in which a floater floats on a liquid-phase fuel to allow a resistance value to be changed depending on a height change of the floater and an electronic liquid level sensor directly detecting a height of a liquid-phase fuel without using a separate floater. Among them, the mechanical liquid level sensor has been currently used widely due to a cheap cost.
FIGS. 1 and 2 are perspective views illustrating a liquid level sensor for a fuel tank according to the related art. The liquid level sensor for a fuel tank according to the related art is configured to include a case 10, a resistor substrate 20 provided in the case 10 and formed radially in a predetermined angle range, an arm having one side rotatably coupled to the case 10 and the other side coupled to a floater, and a wiper 40 coupled to the arm so as to be rotated together with the arm and contacting the resistor substrate 20, as illustrated in FIGS. 1 and 2. Here, one side of the arm is coupled and fixed to an arm installation rotating body 60 of which a shaft is coupled to the case 10, and the wiper 40 is coupled to the shaft. Therefore, the arm installation rotating body 60 and the wiper 40 may also be configured to be rotated together with the arm depending on rotation of the arm.
In the liquid level sensor for a fuel tank according to the related art configured as described above, the case 10 is fixed to be disposed in the fuel tank, and the floater ascends and descends depending on a liquid level of a fuel, such that the wiper 40 is rotated together with the arm 30.
Therefore, a contact protrusion of the wiper 40 contacts different positions of the resistor substrate 20 while being rotated within a predetermined angle in a state in which it contacts a circuit pattern of the resistor substrate 20, and the resistor substrate 20 variably represents a resistance value depending on a residual amount of the fuel, thereby making it possible to display the residual amount of the fuel on an instrument panel of the vehicle.
However, in the liquid level sensor a fuel tank according to the related art, since a contact portion between the resistor substrate and the wiper contacting each other to represent different resistance values are exposed to the fuel or the air, when the contact portion between the resistor substrate and the wiper is made of a silver based material containing a large amount of silver (Ag) component, the contact portion is easily oxidized and corroded by a sulfur component of the fuel. Furthermore, abrasion occurs due to a continuous contact between the resistor substrate and the wiper to reduce durability, such that it is difficult to detect an accurate residual amount of the fuel. In addition, recently, a bio-fuel, or the like, has been developed and used. However, the corrosion and the abrasion as described above may be more rapidly made at the time of using the bio-fuel.
In order to solve the problems described above, a technology of injecting a liquid (hereinafter, referred to as a “filled liquid”) that may perform lubrication and anti-corrosion actions into an internal space of the case in which the resistor substrate and the wiper are positioned and closing the case has been developed. Therefore, the resistor substrate and the wipers do not contact the fuel within the fuel tank, and an abrasion phenomenon due to friction between the resistor substrate and the wiper does not occur.
However, in the liquid level sensor for a fuel tank of which the case is closed in a state in which the filled liquid is filled in the case, when a pressure difference between the inner portion and an outer portion of the case is generated due to a pressure change, a temperature change, or the like, of the outer portion of the case, the case is deformed or damaged, such that there is the possibility that the filled liquid in the case will be leaked to the outer portion of the case. In addition, in the case in which the arm or the shaft coupled to the arm penetrates through the case to thereby be rotatably coupled to the case, when a pressure difference between the inner portion and the outer portion of the closed case is generated, the filled liquid in the case may be leaked to the outer portion of the case through a space between the arm or the shaft and a sealing member contacting each other.
In this case, durability of the wiper and the resistor substrate is reduced, and reliability of detection of a fuel flow rate is also reduced.